#include<iostream>
#include<algorithm>
using namespace std;
	

int main()
{
	int n;
	int data[200];
	for(int i=0; i<200; i++)
	{
		data[i] = 4 * i + 6;
	}
	cin >> n;
	int left = 0, right = 200;
	while(left < right)
	{
		int mid =  left + (right - left) / 2;
		if(data[mid] < n)
		{
			left = mid + 1;
		}
		else
		{
			right = mid;
		}
	}
	cout << left << endl;
}
